WASHINGTON -- Lois Lerner, the head of the IRS office under fire for improperly targeting conservative groups, was replaced by the agency's acting commissioner on Thursday, a day after she insisted she had done nothing wrong and refused to answer questions before a congressional committee.

The Internal Revenue Service warned about a telephone scam in which targeted taxpayers are told they owe money and must pay up immediately.
The IRS on Thursday said the operation was sophisticated. The scammers are able to provide would-be victims the...